Hydroprocessing or hydrotreatment to remove undesirable components from hydrocarbon feed streams is a well-known method of catalytically treating such heavy hydrocarbons to increase their commercial value. "Heavy" hydrocarbon liquid streams, and particularly reduced crude oils, petroleum residual tar sand bitumen, shale oil or liquified coal or reclaimed oil, generally contain product contaminants, such as sulfur, and/or nitrogen, metals and organo-metallic compounds that tend to deactivate catalyst particles during contact by the feed stream and hydrogen under hydroprocessing conditions. Such hydroprocessing conditions are normally in the range of 212.degree. F. to 1200.degree. F. (100.degree. to 650.degree. C.) at pressures of from 20 to 300 atmospheres. Generally such hydroprocessing is in the presence of catalyst containing Group VI or VIII metals such as platinum, molybdenum, tungsten, nickel, cobalt, etc., in combination with various other oxide particles of alumina, silica, magnesia and so forth having a high surface to volume ratio. More specifically, catalyst utilized for hydrodemetalation, hydrodesulfurization, hydrodenitrification, hydrocracking etc., of heavy oils and the like are generally made up of a carrier or base material; such as alumina, silica, silica-alumina, or possibly, crystalline aluminosilicate, with one or more promoter(s) or catalytically active metal(s) (or compound(s)) plus trace materials. Typical catalytically active metals utilized are cobalt, molybdenum, nickel and tungsten; however, other metals or compounds could be selected dependent on the application.
The packed bed of hydroprocessing catalyst in contact with upward-flowing fluid charge, such as a hydrocarbon feed and a hydrogen-containing gas, is generally supported by the catalyst support structure which serves both to support the packed bed of catalysts and to aid in achieving a uniform distribution of upflowing fluid into the catalyst bed. Failure to achieve an adequate distribution of fluid into the bed may lead to rapid catalyst deactivation or the formation of solid deposits in the catalyst bed.
A number of solutions have been proposed for improving the distribution of liquid and gaseous reactants into a catalyst bed.
U.S. Pat. No 3,336,217 to Meaux teaches a method for intermittently withdrawing catalyst from the bed of a high pressure and temperature reactor, in which the catalyst is supported in the bed on a conventional bubble cap tray or other suitable means. Additional disclosures of a perforated catalyst partition having bubble caps include U.S. Pat. Nos. 3,197,288; 3,410,791; 3,410,792; 3,523,888 and 4,738,770.
U.S. Pat. No. 4,312,741 to Jacquin teaches a catalytic process for conversion of hydrocarbons or bituminous shales or carbon monoxide in the liquid phase in contact with upward flowing hydrogen. The reactor used in the process includes one or more stages, at the bottom of each being a perforated support with multiple openings having a cross-section of a size smaller than the catalyst particle and at least one opening of a cross-section substantially larger than the catalyst particles. A fluid (hydrocarbon and/or hydrogen) is injected upward through the large opening to prevent rapid flow of catalyst through the opening. Catalyst may be removed from the reactor by stopping the fluid flow and allowing catalyst to fall through the support.
U.S. Pat. No. 4,392,943 to Euzen, et al. teaches a process for catalytic treatment of hydrocarbon in the presence of hydrogen where the catalyst is introduced at the top of a reactor vessel and withdrawn from the bottom, countercurrent with the hydrocarbon which is introduced at the bottom and discharged from the top. Catalyst discharge occurs through a flared funnel within the reactor. The funnel allows for the upward flow of hydrocarbon through perforations of a size sufficiently small to prevent passage of the catalyst downward through the perforations. Hydrocarbon is injected into the reactor through a delivery tube having orifices located either above and/or below the cone.
U.S. Pat. No. 4,444,653 to Euzen et al. teaches a process for withdrawing granulated solid particles from and introducing fluid into a reactor having a flared zone for withdrawing catalyst and a pipe system for injecting fluid above the walls of the flared zone. The flared zone is a continuous (i.e. free of roughness and of any openings) structure having the shape of an overturned cone or pyramid whose apex is oriented downward. The angle of the cone axis with one of the cone generatrices is between 10.degree. and 80.degree., and preferably between 30.degree. and 40.degree.. The pipe system for injecting fluids into the reactor may include a series of pipes connected at one end and radiating out along the funnel, arranged as the ribs of an overturned umbrella. The cross-sectional area of the different injection tubes in the pipe system are designed to eliminate vapor-liquid phase separation. The perforations or slots in the injection tubes are preferentially oriented downwards to avoid their clogging with catalyst particles.
U.S. Pat. No. 4,571,326 to Bischoff et al. teaches an apparatus for withdrawing solid particles and introducing a fluid charge into the contact zone of a reactor. As part of the apparatus, a withdrawing funnel of inverted conical pyramidal shape is included in the reactor. The withdrawing funnel is provided with perforations or slots distributed over its surface, with the size of the perforations being small enough to prevent passage of catalyst particles while permitting the passage of an ascending stream of fluid. To avoid the migration of reactant gas below the upper part of the funnel, the gas is caused to pass through parallel paths, which oblige the gas particles to follow a controlled path below the funnels.
U.S. Pat. No. 4,639,354 to Bischoff et al. teaches a horizontal tray having regularly spaced openings, each of a sufficiently small size to prevent solid particles from passing through but of sufficient size to give access to an ascending stream of fluid charge and hydrogen.
U.S. Pat. No. 4,968,409 to Smith describes a feed distribution system for selectively upgrading a feed stream of hydrocarbon fluid containing metallic components which counterflow into a descending bed of catalyst particles. The system includes a reactor vessel and an inclined surface, such as a conical support member, for the descending bed of catalyst particles. Gas distribution to the bottom of the inclined surface is through a plurality of holes formed at different elevations, so that gas flow into the bed is substantially uniform, independent of hole elevation or elevation of liquid feed tubes interconnecting a common liquid reservoir to the catalyst bed through the inclined surface. Thus, uniform dispersion of both the gaseous components and the liquid hydrocarbonaceous components is maintained into the descending bed of catalyst particles. Desirably, the conical surface is disposed so that the apex extends downwardly relative to the feed.
U.S. Pat. No. 5,076,908 to Stangeland, et al. teaches continuously supplying replacement catalyst to a downwardly flowing catalyst bed in a hydrocarbon feed stream upflowing at a rate controlled to prevent substantial ebulation of the catalyst particles forming the packed bed. The conventional catalyst support structure, as taught in Stangeland et al. (U.S. Pat. No. 5,076,908), is a beam-supported structure. This structure includes a series of annular polygons, approaching the form of annular rings, formed by a plurality of segment plates extending from an imperforate center plate to the sidewall of the reactor vessel, and radial spoke support members extending between the segment plates. This assembly supports a conical, or pyramidal, perforated plate or screen, which is permeable to both gas and liquid rising from the lower portion of the reactor vessel. With this particular structure, the mixture of the hydrocarbon liquid feed and hydrogen gas entering the bed separates by gravity into radially alternate gas and liquid rings, made up of adjacent segments between each pair or radial spokes. Thus, both phases flow upwardly through alternate concentric annular passages under the screen.
However, in the conventional catalyst support structure taught in U.S. Pat. No. 5,076,908, the weight and size of the beams in the structure increase dramatically as reactor size increases. The increased weight and size both increases the complexity and cost of fabrication and installation, and tend to hinder fluid from being uniformly distributed into the catalyst bed.
While a number of solutions have been proposed to improve the distribution of upflowing fluids into a catalyst bed, none have been completely satisfactory. Therefore, it is a particular object of this invention to provide a catalyst support structure for the improved distribution of upflowing fluid components into a downflowing catalyst reaction bed.
It Is a further object of this invention is to provide a catalyst support structure having improved capabilities for uniformly distributing hydrogen-containing gas and a liquid feedstock into a bed or layer of catalytic particulates. It is a further object of this invention to provide a catalyst support structure which facilitates removal of catalyst from a catalytic reactor.
It is a further object of the invention to provide an easily manufacturable and light-weight support structure suitable for supporting a moving catalyst bed in a large diameter reactor, while introducing fluid into the catalyst bed in a uniform distribution.